FMeXtra is a dead thing. Years ago some radiostations had added these signals to their FM transmitters. To put extra radiostations together with their FM main station. But it seems like it didn't went more than a test. Broadcast Partners in The Netherlands (Hans know this company) sold radio's to receive this signals. The showed it at IBC convention in Amsterdam that year. They had an implementation to add these signals to their transmitters, but now I talk about something from the past. Just checked it's already eight years ago...
DRM is another technique to change AM modulated radiostations into digital. I thought there are still stations which use this, although not many listeners because of a lack of sold radiogear. DAB+ has more listeners